Most people get their cars oil changed by someone else. Could this job be done yourself? Of course it can, its not very complicated, however, given the choice between spending the effort to do the job, or paying someone a modest fee, people usually pay someone to do it.
ScoutKing, I don't know how old you are, but I'm sure you aren't to the point of financial security. In your 'reality', the value of a dollar is much higher because you either don't make much, or don't make at all, therefore you are more inclined to do a thing yourself if you have the means. Brainjuice has the means to make a Gmod video, anyone has the means, however, Brainjuice's time is obviously worth more than the money he is willing to give you. Maybe you don't understand this concept yet, but this is called capitalism; he is willing to give you a monetary prize for your labor.
-This is fine, in fact, its more than fine, it's how anything gets done in the world!-
However, you told Brainjuice that (with the assumption that he has your same value for money), that it would be better if he did it himself. What you didn't tell him is that it takes X amount of effort and time. Do you know his situation? Do you know his level of computer literacy? Of course not, because you didn't bother asking. You assumed that he understands gaming environments nearly as well as you do, and that he would be able to create screenshots (which is not what he wanted) fairly quickly. Given the proper amount of time to acclimate yourself to Gmod can take a while as there is no other game like it, but putting a novice in this place takes even longer.
To make matters worse, you've also driven away a potential business opportunity (hense the entrepreneurial comment). Imagine if you did make a video for Brainjuice and were paid for it. Now imagine if this video got used like he said it would and it made a great impression on the viewers to the point where they wanted a video of their own. What do you think would happen next? Do you think they'll come to this site and learn how to make their own if they have the means to pay instead? Of course not. Its easier to pay someone when you have money to pay with.
Also, please read the above before you reply...
I couldn't have said it better myself.